In the development of the diagnostics field, there has been explosive growth in the number of substances to be determined. For the most part, the medical field has looked to clinical laboratories for these determinations. The clinical laboratories have been dependent upon expensive sophisticated equipment and highly trained technical help to fulfill the manifold needs of the medical community. However, in a highly automated clinical laboratory, there is substantial need to perform one or a few assays on a stat basis with minimum equipment.
There is also an expanding need for having analytical capabilities in doctors' offices and in the home. There is a continuing need to monitor the level of drug administered to people with chronic illnesses, such as diabetics, asthmatics, epileptics, and cardiac patients, as it appears in a physiological fluid, such as blood. Tests of interest include prothrombin time, potassium ion, and cholesterol. Determining red-blood-cell count is also a common test. In the case of diabetic patients, it is necessary to determine sugar level in urine or blood.
Numerous approaches have been developed toward this end, depending to verying degrees on instrumental or visual observation of the result. Typical of these are the so called "dip-stick" methods. These methods generally employ a plastic strip with a reagent-containing matrix layered thereon. Sample is applied to the strip and the presence or absence of a analyte is indicated by a color-forming reaction. While such devices have proven useful for the qualitative determination of the presence of analytes in urine and can even be used for rough quantitative analysis, they are not particularly useful with whole blood because of the interferring effects of red blood cells, nor are they useful for making fine quantitative distinctions. Accordingly, there remains a need for the development of methods and devices capable of analyzing whole blood and other complex samples rapidly with a minimum of user manipulations.
Many small devices in the analytical area depend on the use of plastics having specified characteristics, such as optical transparency and machinability. Machinability refers here to the ability to produce chambers, channels, and openings of prescribed dimensions within the plastic device. Although numerous plastic devices have been devised, the fabrication techniques are not interchangeable because of differences in the devices or the desired measuring result. This is particularly true for devices containing channels or other chambers of small dimensions internally in the plastic material. The fine channels are difficult to produce entirely within a plastic matrix and, if prepared in the surface of two matrices to be sealed to each other, are readily deformed during many sealing processes.
Accordingly, there remains a need for new devices for use in methods of rapid analytical testing and for new methods of producing these devices.